A well-known form of harvesting machine is a rotary combine. A typical combine includes a crop harvesting apparatus which reaps grain stalks and other plant materials and feed them to a threshing apparatus. The grain stalks or other crop and plant materials harvested in the field are moved rearwardly from a crop harvesting header assembly and introduced for threshing to the threshing apparatus by a crop feeder assembly.
The threshing apparatus typically includes a generally tubular rotor housing mounted in the combine body. One or more rotors are supported for rotation within the housing. The housing and the rotor or rotors have cooperating infeed or inlet sections, threshing sections, and optionally separating sections, the inlet sections being operable during rotation of the rotor or rotors, for receiving the crop material from the feeder assembly, and conveying the crop material to the threshing section. The threshing section threshes the crop, and feeds it to the separating section, with the grain and other smaller elements of the crop falling through a perforated concave that forms part of the rotor housing extending around the rotor or rotors.
The ability to transfer crop materials from the inlet section to the threshing section is a key to efficient combine operations. During harvesting operations, the generally linear movement of the crop materials received from the feeder assembly is converted in the inlet section into a rotating, circulatory movement, in a rearward and outward direction.
The inlet section of a rotor typically has several helical inlet impellers or flights therearound, operable for propelling the crop material radially outwardly and to the threshing section during rotation of the rotor. As a general rule, the greater the number of impellers, the greater the crop material capacity and infeed capability. The threshing section has an array or layout of threshing elements arranged in one or more predetermined patterns therearound and along the length thereof. The threshing elements typically include a first row or rank of rasp bars disposed around the rotor adjacent the inlet section. These rasp bars, and supporting structure thereof, function to direct or press the crop material radially outwardly against the inner peripheral surface of the housing, and the conveying action of the inlet impellers, the shape of the housing surface, guide bars on the housing surface, and the rasp bars, cooperate for forming the crop material into a mat, and initiate conveying the mat along a generally helical path around the rotor, through an annular gap or space between the rotor and the surface. The rasp bars typically include features on the radial outer surfaces thereof, such as serrations or the like, which cooperate with features on the housing surface, including the guide bars, for threshing the crop material in essentially a raking action, while conveying it along. Typically, the greater the number of rasp bars, and the greater surface area thereof, the more aggressive the threshing action, for given conditions such as speed of rotation of the rotor, gap size, and crop type, volume and condition.
Commonly, the layout of the first row or rank of rasp bars closest to the inlet section equally spaces the rasp bars around the rotor for balance, and provides a number of rasp bars equal to and in alignment with the inlet impellers or flights. For example, a rotor including two impellers may have a first row of rasp bars including two rasp bars. A rotor including four impellers may have a first row having four rasp bars. These first rasp bars are typically positioned immediately adjacent to the end of the helical impellers, respectively, and are aligned therewith for engaging the crop material conveyed by the respective impeller and initially forming the crop material mat against the surface of the housing, threshing it, and conveying it along a helical path in the space or gap between the rotor and the housing surface. Reference in this regard, DeBusscher et al., U.S. Pat. No. 4,248,248, which illustrates a representative inlet impeller and rasp bar relationship.
It has been observed that, if the number of rasp bars in the first row exceeds the number of impellers feeding the crop material, or if one or more of the rasp bars are not carefully aligned with an associated impeller, such rasp bars not associated with an impeller may act to obstruct or block a portion of the crop material flow, and thus can interfere with and degrade the feeding of the crop material to the threshing section. However, in some instances wherein it is desired to utilize four impellers, it has been found that having a corresponding four rasp bars in the first row or rank can provide a more aggressive than desired threshing capability, particularly if it is desired or required to rotate the rotor at higher speeds, such as when threshing some smaller grains and under higher flow rate conditions. Using a layout including a number of rasp bars in the first row equal to the number of impellers, e.g., four, is also more expensive than using a lesser number.
Thus, what is sought is a rotor impeller and rasp bar layout that overcomes one or more of the shortcomings set forth above, and which is advantageous costwise.